The present invention relates to a tracer control system, and more particularly to a tracer control system which is suitable for tracing a concavity of a model.
A tracer control system is well known as a control system which traces the surface of a model with a tracer head and, while doing so, controls the position of a tool such as a cutter or the like in accordance with a displacement signal from the tracer head, thereby cutting a workpiece into the same shape as that of the model.
Conventionally known as methods for tracing a concavity of a model are clamped tracer control systems disclosed in Pat. Applns. Nos. 10228/79 and 145330/81 filed by the present applicant. The clamped tracer control system moves the tip of the tracer head (a stylus) in a predetermined direction while holding (clamping) it at a predetermined depth from the top surface of a model along the inner wall of its concavity (that is, while holding the tip of the tracer head apart from the bottom of the concavity). When the tip of the tracer head moves into contact with the inner wall of the concavity again on the opposite side thereof, it is brought up to the top surface of the model along the inner wall, and then repeats this operation over the entire area of the concavity while effecting a pick feed on the top surface of the model for each stroke while holding the tip of the tracer head at the abovesaid depth (a clamp level) in the concavity. There is thereby formed in the workpiece a concavity of a uniform depth equal to the abovesaid clamp level.
With the above clamped tracer control system, however, each time the clamp level is increased, the already machined upper portion of the inner wall of the workpiece is machined (that is, the cutter is brought into contact with that portion), presenting problems of not only involving a waste of the cutting time but also shortening the service life of the cutter owing to its repeated rubbing against the already machined inner wall of the workpiece.